A rail system including an adjustable detector. A rail unit is elongated in a longitudinal direction, and includes first and second rails which are spaced apart from each other in a horizontal direction and are fixed to the ground. An X-ray tube stand is movable in a lateral direction with respect to the rail unit, and is provided therein with a vertically-movable tube arm and an X-ray generator which is rotatably disposed on one end of the tube arm. A C-shaped X-ray photography table is spaced apart from the rail unit. An X-ray sensor stand is movable in a lateral direction with respect to the rail unit, and moves an X-ray detector disposed therein into a hollow space in the lower part of the X-ray photography table such that the centers of the X-ray detector and the X-ray photography table are positioned at the same point.
